Durant Drake, Arthur Oncken Lovejoy, James Bissett Pratt, Arthur Kenyon Rogers, George Santayana (1920). “Essays in critical realism: a co-operative study of the problem of knowledge”
George Santayana, Marianne S. Wokeck, Martin A. Coleman, James Gouinlock (2015). “The Life of Reason Or The Phases of Human Progress: Reason in Art, Volume VII, Book Four”, p.107, MIT Press
George Santayana (1937). “The Works of George Santayana: Character and opinion in the United States. The genteel tradition at bay. Dewey's naturalistic metaphysics. Philosophical heresy”